An angular ball bearing which is illustrated as an example in FIG. 3 is of a type that both the inner ring 1 and outer ring 2 thereof have a counter-bore. A plurality of balls 3 intervene between the raceway surface 1a of the inner ring 1 and the raceway surface 2a of the outer ring 2 and are retained by a cage 4'. The straight line (the contacting angle line L) which connects the balls 3 to the raceway surfaces 1a,2a of the inner and outer rings 1,2 has a certain angle (contact angle .theta.) with respect to the radial direction, whereby these balls 3 are constructed so that the same are able to receive a radial load and an axial load in one direction.
The cage 4' is a molded resin (flexing molding, injection molding, etc.) made of laminated phenol resin, reinforced synthetic resin, etc., and is provided with a plurality of pockets 4'a in which the balls 3 are housed.
As enlarged and shown in FIG. 4, the wall surface of the pocket 4'a is drawn with a spherical surface 4'a1 having a radius R of curvature obtained by adding the pocket clearance (corresponding to one side) to the radius (Dw/2) with the point 0 (the intersection of the pitch circle of the ball 3 and the contact angle line L) made its center of curvature. The inlet diameter A' at the outer side of the pocket 4'a is made smaller than the diameter (Dw) of the ball 3. (That is, A'&lt;Dw).
As shown in FIG. 5, when assembling, a cage 4' is attached to the inner ring 1, balls 3 are pressed into the pocket 4'a of the cage 4' from the outer side with both the cage 4' and the inner ring 1 laid down, whereby the balls 3 are inserted into the pocket 4'a by elastically and forcibly widening the inlet diameter A' with the balls 3.
In a conventional cage 4', since the inlet diameter A' of the pocket 4'a is made smaller than the diameter Dw of the balls 3, it is necessary to provide an insertion force F to widen the inlet diameter A' of the pocket 4'a in an insertion work of balls 3. Although this insertion force F does not constitute a large problem in a case where the bearing size is small, a comparatively large force is required if the bearing size is increased. Furthermore, unless the balls 3 are completely inserted, some of the balls 3 may be pushed out of the pockets 4'a and may be dropped out during the assembling.